This invention relates to a mandrel, a method of making the mandrel and orifice plates electroformed using the mandrel. The orifice plate that is formed has a thin orifice area surrounded by a thicker border. The thinner orifice area allows more orifices to be packed into a given area while the thicker border allows the orifice plate to withstand the rigors of manufacturing.
A prior-art mandrel for electroforming orifice plates has a substrate of glass, plastic or a polished silicon wafer. A thin film layer of conductive material is deposited on this substrate. The conductive material is typically of chrome and stainless steel. A layer of dielectric is deposited on the conductive layer. This dielectric layer is of a nonconductive material such as silicon carbide. Patterns on the dielectric layer are lithographically formed using conventional masking, ultraviolet exposure and etching techniques to dimensionally define a molding surface for molding orifices in orifice plates. U.S. Pat. No. 4,773,971 discloses a method of making such a mandrel.
Orifice plates are formed on a mandrel in an electroforming process. The orifice plates thus formed are all on a single sheet. Breaking tabs that are also electroformed on the sheet defines the boundaries of each orifice plate. In the manufacturing of printheads, the sheet of orifice plates is attached to a mounting tape, for example, the Nitto Denko Elep Holder type V-8T available from Nitto Denko Corporation, Tokyo, Japan. The orifice plates are next singulated into individual orifice plates by breaking the sheet along the breaking tabs. The mounting tape holds the singulated orifice plates for further processing. A machine next picks and places each orifice plate over a corresponding printhead die on a wafer containing many such dies. The wafer and attached orifice plates are put through a xe2x80x9cstake and bakexe2x80x9d process to cause the orifice plates to adhere to the dies. After the xe2x80x9cstake and bakexe2x80x9d process, each printhead consisting of a die and an orifice plate is singulated using dice sawing. Each complete pair of orifice plate and printhead die is then ready for attaching to a pen body to complete the fabrication of an ink-jet pen. This pen body typically contains an ink reservoir which supplies ink to the printhead. In such a manufacturing process, the orifice plates are subjected to considerably rough handling during the steps of singulation and attachment to the printhead dies.
To withstand such rigors in the manufacturing process, the orifice plates will have to be of a certain minimum thickness. As the size of an orifice is directly proportional to the thickness of an orifice plate due to the electroforming process, the thicker the orifice plate, the larger will be the orifices. These larger orifices will mean that fewer orifices can be packed into a given area, thus limiting the orifice count and resolution of an orifice plate. It is therefore desirable to keep the orifice plate thin so as to allow more orifices to be packed into a given area, since the orifices will be relatively smaller. However, this desirability contradicts the requirement to keep the orifice plates sufficiently thick for reasons previously discussed.
Prior art mandrels can only form orifice plates that are substantially uniformly thick. There is therefore the need for a new mandrel and method for electroforming orifice plates of a non-uniform thickness.
In one aspect of the present invention, a mandrel according to one embodiment has a metallic layer on a substrate. The metallic layer has a first molding surface that is electrically isolated from a second molding surface. The second molding surface is for substantially electroforming an orifice area of an orifice plate. The first molding surface is for substantially electroforming portions on the orifice plate that are thicker than the orifice area. These thicker portions are preferably portions that form a border around the orifice area. The mandrel also has means for electroforming orifices in the orifice area. In use, the first molding surface is predominantly allowed to electroform the thicker portions without the second molding surface electroforming the orifice area. As the thicker portions build up, they electrically connect the first and the second molding surfaces to allow the second molding surface to subsequently electroform the orifice area. The orifice plate thus formed is non-uniformly thick.
In another aspect of the present invention, a preferred method of making the above mandrel involves depositing a metallic layer on a substrate followed by depositing a first photoresist layer on the metallic layer. Next, a first photomask having a first pattern is positioned on the first photoresist layer. The first photomask and the first photoresist layer are exposed to ultraviolet light for a predetermined period. After the exposure, the first photoresist layer is developed to produce the first pattern on the metallic layer. The portions of the metallic layer exposed by the first pattern of the first photomask is then etched to define the first and second molding surfaces. The method also includes introducing means for electroforming orifices in the orifice area. The remaining photoresist layer is stripped from the etched metallic layer. Preferably, introducing means for electroforming orifices in the orifice area involves stripping the remaining first photoresist layer and depositing a dielectric layer on the etched metallic layer followed by depositing a second photoresist layer on the dielectric layer. A second photomask having a second pattern is positioned on the second photoresist layer. Similarly, the second photomask and the second photoresist layer are exposed to ultraviolet light. Again, after exposure, the second photoresist layer is developed to produce the second pattern on the dielectric layer. The portions of the dielectric layer that are exposed by the second pattern are etched to define the dielectric areas.
In yet another aspect, an orifice plate electroformed using the above mandrel has an orifice area and portions that are thicker than the orifice area. The orifice area has orifices electroformed on it. The thicker portions are preferably portions of the orifice plate that form a border surrounding the orifice area.